1. Field of the invention
The invention relates in general to robot mechanisms including serial link structures utilizing revolute joints, such as mechanical manipulators, robotic grippers and appendages for use in robotics applications.
2. The Prior Art
Robot mechanisms including serial link structures utilizing revolute joints include robotic grippers that are generally connected at the end of robotic arms. Robotic grippers that are constructed with links and joints that act similarly to fingers are susceptible to damage. It is easy to accidently break the fingers of robotic grippers if the robot knocks the fingers against hard surfaces. This is particularly likely where robots are used in unstructured environments where the feedback systems and dynamic control of the robot may not be able to prevent such accidents.
Potential solutions include making robotic grippers and fingers very strong or very flexible. Both solutions have been implemented. Increased strength usually results in increased weight and cost, both of which negatively affect the performance and market viability of the robotic grippers. Another alternative is increasing the flexibility of the fingers, but that trades off stiffness for flexibility, which can have negative performance impacts in the functionality of the robotic gripper.
Robotic grippers can be separated into two classes, intrinsic and extrinsic robotic grippers. Intrinsic robotic grippers have the motors in or close to the joints they are controlling. Extrinsic robotic grippers usually use some type of tendon or cable between the joints they are controlling and an actuator that is located away from the joints.
A solution for protecting fingers from damage has been developed using magnets to hold the finger to the palm of the robotic gripper, but “break-away” from the palm if the fingers are strongly impacted. This solution does a good job of protecting the finger from damage while maintaining good finger structural properties. However, this solution has both the finger and motor on the “break-away” portion of the finger, which is more similar to an intrinsic finger design.
A weakness of this design is that the power that can be applied through the finger is limited by the strength of the magnetic connection between the finger and the robotic gripper. Thus a very powerful finger requires a very strong magnetic connection to the palm of the robotic gripper. The stronger the magnetic field in the palm of the robotic gripper, the stronger the magnetic interaction with the operational environment of the robot, which can have negative consequences in attracting ferromagnetic components or particles or interfering with magnetically sensitive equipment.
Another weakness of the existing approach to magnetic finger attachment is that if the finger is knocked off the palm of the robotic gripper, the finger is no longer attached to the robot and cannot be easily reattached without human intervention or a very intelligent robot. For example, if a robot is operating at a contaminated disaster site where humans cannot operate and the finger is knocked off, there is significant overhead to retrieve the finger and replace it onto the palm.
In the existing magnetic attachment of fingers, the force of the load on the finger is wholly supported by the magnets. Since there are two types of forces acting on the finger, desired load and undesired load (unintentional impact), the fingers are far more likely to fall off while under desired load. When the fingers are not under load, they have a very strong force keeping them attached to the robotic gripper. This limits their protection when they most need it.
Finally, the prior art for magnetic attachment of fingers in robotic grippers does not apply to extrinsic architectures that use tendons for transmitting power to joints.